The accurate determination of oil saturation is an essential part of reservoir petrophysical evaluation. Both C/H and C/O logging methods are primarily used to determine oil saturation in low-salinity reservoirs.

The study aims to compare the logging response effects of the C/H and C/O methods.

Firstly, a spherical model and the model set by the C/O logging instrument RPM (Halliburton Company) were applied to Monte Carlo simulations, and the window counts of the atoms formed under different geological parameters and pore structures were calculated by MCNP5. Then, the relationship between C/O and C/H with saturation and the sensitivity to saturation were analyzed, and the response effects of C/O and C/H were compared. Finally, the mechanisms underlying the different response effects of C/H under different models were clarified.

The analysis results show that C/H and C/O exhibit the same relationship with porosity and saturation in casing wells, and both can be used to calculate saturation. However, compared to C/O, C/H is more affected by the borehole environment and is less sensitive to saturation; therefore, it is not suitable for saturation calculations in complex boreholes.